Advanced Materials

The cover depicts polymer “microfins” embedded in pH-responsive gel and submerged in water. Actuation of the fins driven by volume phase transitions in a pH-responsive hydrogel “muscle” may be able to drive the flow of particles in solution, as proposed on p. 1442 by Joanna Aizenberg and co-workers. The system is designed to provide uniform directional bending actuation over a large area and integrated with electrochemical and microfluidic cells.

While chiral nematic liquid crystals are promising for a variety of dynamic photonic applications, their contrast is usually limited to 50%. Timothy J. Bunning and co-workers present a system that dynamically induces contrast approaching 100% at multiple wavelengths using temperature on p. 1453. The inside cover is a rendered graphic of a surface bound helicoidal structured polymer network that templates the local liquid crystal molecules. The green background is a color enhanced polarized optical microscopy image of the liquid crystal texture in the non-templated region that is critical to thermal tuning behavior. Cover design by Michael E. McConney.

Two-photon absorption (TPA) efficiency – scale corrected – as a function of the number of effective electrons, N_eff, for the N-core organometallics dendrimers reported by Roberts et. al. (1, 2, 3; spheres); which are two orders of magnitude more efficient than the N-core organic dendrimers (G0, G1, G2; hexagons) used for comparison.

The two-photon absorption cross-sections of related organometallic and organic dendrimers have been compared using a basket of scaling factors, the results revealing that organometallics are highly competitive as possible nonlinear optical materials viewed from economic, size, and weight perspectives, as well as consideration of π-electron contribution.

Highly efficient deep blue phosphorescent organic light-emitting diodes (PHOLEDs) with external quantum efficiency above 20% are developed using a bipolar-type high-triplet-energy host material and a high-triplet-energy exciton blocking material. Maximum quantum efficiency of 25.1% and low roll-off (still 23.1% at 1000 cd m⁻²) are achieved in these deep blue PHOLEDs.

A bio-inspired hybrid materials system has been developed by utilizing pH-responsive, poly(acrylic acid-co-acrylamide) hydrogel as the “muscle” that dynamically and reversibly actuates the embedded microposts and microfins while the sample is submerged. The system is designed to provide uniform directional bending actuation over a large area and integrated with electrochemical and microfluidic cells.

Source and drain functionalization with a light-responsive azobenzene-based self-assembled monolayer (SAM) is used to modulate the charge injection at the Au electrode–semiconductor interface of an organic field-effect transistor (OFET). This photochromic bistable SAM mediates the injection through the variation of the tunneling barrier across the SAM.

A dynamic multicolored cholesteric cell is formed using chiral, structured, surface-tethered polymer networks. The multicolored cholesteric cell is filled with a thermally tunable liquid crystal mixture of opposite handedness of the polymer networks, which enables thermally induced hyper-reflectivity at the two reflection bands induced by the surface tethered polymer.

Phononic crystals are acoustic metamaterials that are used to shape fluid droplets by controlling their interaction with acoustic waves in a manner tunable by the frequency of the excitation. By shaping the field generated by surface acoustic waves (SAWs), a precise control over the direction and the amplitude of the interfacial jetting of a sessile drop of liquid on non-piezoelectric materials is demonstrated.

Various intrinsically colored and luminescent silks are produced in vivo through the direct uptake of dyes into silkworms. A better understanding is established to select and design functional materials for effective uptake into silk fibroin by controlling structure-dependent hydrophobicity and self-assembly capabilities.

A free-standing Pt-nanowire membrane fabricated via a multistep templating process is used as an electrocatalyst for the oxygen reduction reaction (ORR). It exhibits remarkably high stability and good catalytic activity due to its unique nanowire-network structure.

A microfluidic system was used to prepare a large number of size-controlled collagen gel beads to form microtissue units, “cell beads”, as tissue building blocks. By stacking cell beads into a doll-shaped silicone chamber, millimeter-thick tissue with uniform cell density was formed rapidly. The bead structure allowed the application into the 3D printing, achieving automated geometrical control of the formed tissues for the fabrication of functional complex tissues. on p. H90

The number of applications of nano materials in cancer diagnosis and therapy is increasing everyday, providing non-invasive methods to approach cancer treatment. This review describes the tumor properties and physicochemical parameters that are important for tumor-targeted nanoparticle design. It provides an overview of different types of state-of-the-art nanoparticles, and identifies opportunities for the further development of nanoparticles as cancer diagnostic and therapeutic agents. on p. H18

The number of applications of nano­materials in cancer diagnosis and therapy is increasing everyday, providing non-invasive methods to approach cancer treatment. This review describes the tumor properties and physicochemical parameters that are important for tumor-targeted nanoparticle design. It provides an overview of different types of state-of-the-art nanoparticles, and identifies opportunities for the further development of nanoparticles as cancer diagnostic and therapeutic agents.

Hydrogel biomaterials based on hyaluronic acid are formed with a wide range of diverse chemistry and processing techniques. This versatility in material design has led to application of these materials in fields of tissue regeneration and drug delivery with structures of gels, fibers, and porous substrates.

A promising platform to realize special biofunctionalities and excellent controllability over the surface properties of smart biointerface materials is provided by the hydrogen-bonding-mediated rever­sible coil/globule transition of a poly(N-isopropylacrylamide) film. Copolymerization with other functional units and/or combination with other materials provide tools for a wide variety of attractive biological and biomedical applications (see graphic).

Robust microfluidic synthesis of polymer nanoparticles based on nanoprecipitation is reported by Omid C. Farokhzad, Rohit Karnik, and co-workers on p. H79. 3D hydrodynamic flow focusing, realized by constructing three sequential inlets for vertical focusing followed by a conventional cross junction for horizontal focusing, isolates the polymer precursors from the channelwalls, both vertically and horizontally.

A versatile microfluidic platform to synthesize NPs by nanoprecipitation using 3D hydrodynamic flow focusing isolates the precipitating precursors from channel walls, eliminating fouling of the channels. It is shown that this new method enables robust nanoprecipitation without polymer aggregation, regardless of the polymer molecular weight or precursor concentration implemented, where the size of the resulting polymeric NPs is tunable.

A novel multifunctional drug–polymer conjugate is prepared. RGD peptide is used to actively target the drug delivery system to tumor neovascular endothelial cells and tumor cells, while the PEG-PAMAM polymeric carrier permits passive targeting to the tumor site by the enhanced permeability and retention (EPR) effect. Controlled release of the anticancer drug doxorubicin is also achieved via acid-sensitive cis-aconityl linkage.

A microfluidic system was used to prepare a large number of size-controlled collagen gel beads to form microtissue units, “cell beads”, as tissue building blocks. By stacking cell beads into a doll-shaped silicone chamber, millimeter-thick tissue with uniform cell density was formed rapidly. The bead structure allowed the application into the 3D printing, achieving automated geometrical control of the formed tissues for the fabrication of functional complex tissues.

Biodegradable elastomeric materials have particular utility in tissue engineering applications because their compliance under force closely resembles the elastic nature of many human tissues. A family of biodegradable poly(ester amide) elastomers were developed, with excellent elasticity under hydrated conditions, good in vivo biocompatibility and a slow degradation rate. This study sheds light on the structure-property relationship behind designing biodegradable elastomeric materials.

A metal-enhanced fluorescence assay enables z-tracking of cell adhesion on surfaces. It is based on a significant enhancement in the fluorescence of labeled bacteria upon approaching a surface and can be used to quantitatively define cell adhesion based on the nanoscale distance between the cells and the surfaces.

Macrophages are recruited at the diseased site in several pathological conditions. Here, we describe a novel method of utilizing their unique properties for targeted drug delivery. Cellular backpacks are designed that ride on macrophage surfaces without affecting cell functions or getting internalized. These backpacks can be used as multimodal therapeutic and diagnostic agents.

Focal adhesions, induced by “matrixbound BMP-2” presented from soft films, are reported by Catherine Picart and co-workers on p. H111. The authors found that C2C12 myoblasts cultured on soft films without BMP-2 were poorly spread and did not exhibit focal adhesions, while the presence of matrix-bound BMP- 2 (image) induced a rapid and drastic increase in cell spreading associated with the presence of focal adhesions.

The dramatic effect of morphogenetic protein 2 (BMP-2), presented to cells in a “matrix bound” manner is described. BMP-2 is either delivered in solution or bound to a thin film made of poly(lysine) and hyaluronan. In this later case only, a striking effect of BMP-2 on cell adhesion and migration is observed.

Injectable and biodegradable gels have been formed by a bottom-up synthesis strategy employing oppositely charged gelatin nanospheres as particulate building blocks. These gels are formed by electrostatic interactions between and tight packing of gelatin nanospheres of opposite charge. Due to their favorable clinical handling, ease of functionalization, and cost-effectiveness, these gels show great potential as injectable gels for tissue regeneration.

A metal-enhanced fluorescence assay enables z-tracking of cell adhesion on surfaces. It is based on a significant enhancement in the fluorescence of labeled bacteria upon approaching a surface and can be used to quantitatively defi ne cell adhesion based on the nanoscale distance between the cells and the surfaces. on p. H101